Headlamp for motor vehicles

ABSTRACT

A headlamp for motor vehicles has a reflector, a gas discharge lamp, a front plate covering a light exit opening of the headlamp, and a filter arranged in a beam path of light beams reflected by the reflector and light beams transmitted directly to the front plate and at least partially absorbing light in a UV wavelength region.

BACKGROUND OF THE INVENTION

The present invention relates to a headlamp for motor vehicles.

More particularly, it relates to a headlamp which has a gas dischargelamp and a front plate which covers the light exit opening of theheadlamp.

Such a headlamp is disclosed in the German Offenlegungsschrift 35 19611. This headlamp has a reflector into which a gas discharge lamp isinserted as a light source. The light exit opening of the headlamp iscovered with a front plate. Apart from visible light, the gas dischargelamp also transmits light in the UV wavelength region of high intensity.This UV light is, on the one hand, noxious and, on the other hand, candestroy plastics and glass. The heat radiation of the gas discharge lampis substantially smaller in comparison with an incandescent lamp so thatmoisture which has penetrated the headlamp or has been precipitated onthe front plate does not dry and moisture which has frozen onto thefront plate does not thaw. In addition, under certain circumstances thelight transmitted by the gas discharge lamp has an excessively high bluefraction.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aheadlamp for motor vehicles which avoids the disadvantages of the priorart.

In keeping with these objects and with others which will become apparenthereinafter, one feature of the present invention resides, brieflystated, in a headlamp in which the beam path of the light beamsreflected by the reflector and the light beams transmitted directly tothe front plate from the gas discharge lamp contains a disc-shapedfilter which is arranged so as to at least partially absorb light in theUV region.

When the headlamp is designed in accordance with the present invention,it has, in contrast with the above, the advantage that the lighttransmitted by the gas discharge lamp in the UV wavelength region isabsorbed by the filter and thus no UV radiation at a harmful intensitycan emerge from the headlamp.

In accordance with another advantageous feature of the presentinvention, the front plate is provided with a coating which absorbslight in the UV wavelength region or consists of a UV light absorbingmaterial and serves as the filter. With such a design of the front plateas a UV filter, a selective heating of the same is achieved so thatduring the operation of the gas discharge lamp moisture which has beenprecipitated on the front plate is dried and moisture which has frozenonto it thaws.

In accordance with another feature of the present invention, the lens isarranged in a holder, and the holder has a component with an electricalline, and the electrical line is interrupted when the lens impactsagainst the component with a specific force, and operation of the gasdischarge lamp is prevented when the line is interrupted. When theheadlamp is designed in accordance with these features it is ensuredthat even with a damaged UV filter no UV radiation emerges from theheadlamp.

It is possible, in accordance with a further development, that the lineis realized as a conductor track mounted on the component, and thecomponent is broken in such a way by the lens when it impacts againstthe component that the conductor track is interrupted. In thisconstruction the line is interrupted in the case of a lens which ismoved out of the holder for example as a result of an impact and thus ina simple manner the failure of the lens is indicated.

Finally, a voltage divider circuit can be provided in the line, and thecontrol device can have an evaluation circuit by means of which theoperation of the gas discharge lamp is prevented in the event of avoltage drop in the line deviating from a voltage drop predetermined bythe voltage divider circuit. In this case, it is ensured that the gasdischarge lamp cannot be operated even with a damaged UV filter due toshort circuiting of the signalling lines.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first exemplary embodiment of a headlamp in longitudinalsection in a greatly simplified view.

FIG. 2 shows second exemplary embodiment of a headlamp in longitudinalsection.

FIG. 3 shows a third exemplary embodiment of a headlamp in longitudinalsection and

FIG. 4 shows a portion, designated in FIG. 3 by IV, in a perspectiveview.

DESCRIPTION OF PREFERRED EMBODIMENTS

In a first exemplary embodiment illustrated in FIG. 1 of a dipped lightheadlamp for motor vehicles, the headlamp has a reflector 8 and a gasdischarge lamp 11 inserted from its rear. The reflector 8 can be in theshape for example of a rotational paraboloid but also divided up into aplurality of different segments and is arranged in a housing 9 made ofplastic. The light exit opening of the headlamp is closed off with afront plate 18 which is constructed as a lens plate. The gas dischargelamp 11 is supplied with the high voltage required for its operation bymeans of an ignition device 20 which is supplied from the electricalsystem of the motor vehicle and actuated by a control device 19. Apartfrom visible light, the gas discharge lamp 11 also transmits light inthe UV wavelength region at a high intensity during its operation. Thefront plate 18 is provided on its inside pointing towards the reflectorwith a coating 23 which at least partially absorbs light in the UVwavelength region. The coating 23 can be formed by means of a thin metallayer for example of gold or chromium. However, the coating 23 can alsobe formed by a fluoride layer. The coating 23 can, for example, beevaporated or sprayed onto the front plate 18. In addition, by means ofthe coating 23 not only is a shielding against UV radiation provided,but it also increases the quality of the glass optics constituted in thefront plate 18 so that an undesired scattering of the light beamspassing through is reduced.

The coating 23 heats up due to the absorbed UV radiation, which leads toa heating up of the front plate 18. Thus, a heating up of the frontplate 18 to accelerate the drying and deicing of the front plate isachieved without the use of extraneous energy. In place of the coating23, the front plate 18 itself can also have the property of absorbing UVlight by appropriate selection of the glass material or by means ofappropriate additives to the glass material. By means of a brownishcolouring of the coating 23 or of the front plate 18 the light emergingfrom the headlamp can be given a colouring so that it has a "warmer"effect. In addition, the coating 23 or the front plate 18 can beconstructed in such a way that blue light is partially absorbed so thatthe light emerging from the headlamp appears less blue.

By means of the colouring of the coating 23 or of the front plate 18heating up of the front plate 18 during operation of the gas dischargelamp 11 is also achieved.

In a variant of the headlamp, instead of constructing the front plate asa UV filter, a disc-shaped filter 22, indicated in FIG. 1 by dashedlines, is arranged between the gas discharge lamp 11 and the front plate18. The filter 22 is provided with a UV light-absorbing coating 23 asdescribed for the front plate above or has the property of absorbing UVlight by means of corresponding selection of material or by means ofadditives to a glass material.

In a second exemplary embodiment illustrated in FIG. 2 of a dipped lightheadlamp for motor vehicles, the lamp has a reflector 10 into which agas discharge lamp 11 is inserted from its rear. In the vertical andhorizontal meridian section of the reflector 10 ellipses are produced,and the axial light arc 12 of the gas discharge lamp 11 is beingarranged in the region of the inner focal point Fe of the ellipses onthe optical axis 13 of the reflector. In the direction of the lightbeams reflected by the reflector 10, a shade 14 with an optically activeupper edge 15 is arranged below the optical axis 13 in the region of theouter focal point Fe' of the ellipses. Furthermore, a lens 17 and afront plate 18 which covers the light exit opening of the headlamp andcan be constructed as a lens plate are arranged in the light exitdirection. During the operation of the gas discharge lamp 11 the lightbeams form an image of the upper edge 15 of the shade 14 via the lens 17as a light/dark border of the light distribution of the headlamp.

The lens 17 serves as a UV filter for shielding the UV light of the gasdischarge lamp 11 and is provided with a coating 23 which absorbs UVlight. The coating 23 can be realised as described in the firstexemplary embodiment. In addition, the lens 17 can also be given UVlight-absorbing properties by means of a suitable glass material or byadditives to the glass material. Alternatively, a disc-shaped UV filter22 can be arranged in the headlamp of the second exemplary embodimentbetween the gas discharge lamp 11 and the front plate 18 or the frontplate 18 can serve as a UV filter by means of a coating 23 or a suitableglass material.

In FIGS. 3 and 4 a third exemplary embodiment of the headlamp isillustrated in which, as in the second exemplary embodiment, the lens 17serves as a UV filter and by means of a coating or a suitable glassmaterial or additives to the glass material has the property ofabsorbing UV light. The gas discharge lamp 11 is inserted by means of alamp carrier 26 into the reflector 10 and covered at its rear with a cap27.

A carrier 28 which extends in the light exit direction and has on itsend pointing away from the reflector 10 a holder 29 for receiving thelens 17 is connected to the front edge of the reflector 10. The carrier28 is realised as a hollow cylinder which is closed at its circumferenceand consists of sheet metal. The reflector 10 forms with the carrier 28and the lens 17 a tight bond so that UV radiation cannot emerge throughthese parts or between them. A frame 31 which has an opening 32 the samesize as the lens 17 for the passage of light is arranged towards thelens plate 18. The lens 17 can be inserted into the carrier 28 from itsend pointing towards the reflector 10 and comes to rest in the lightexit direction against an edge 33 of the carrier 28 forming a part ofthe holder 29 and pointing radially inwards, and against which it isheld by means of a resilient ring 30. The resilient ring 30 is open inits lower region. A stop 36, which is a rivet here, is arranged on thecarrier 28 on one side, here at the top, between which stop and the edge33 the edge of the lens 17 and the resilient ring 30 come to rest in themounted state of the lens. Preferably diametrically opposite, a ceramicplate 34 can be attached to the carrier 28 and projects radially inwardsthrough the open region of the resilient ring 30 when the lens 17 ismounted and engages over the edge of the lens 17 towards the side of thereflector 10. In this arrangement, the ceramic plate 34 could also servefor fixing the position of the lens 17 at this point if the resilientring 30 is dispensed with.

An electrical conductor track 37 is evaporated onto the ceramic plate 34and connected via signalling lines 38 to the electrical control device19 which actuates the ignition device 20. The ceramic plate 34 has apredetermined break point determined by a notch 39, the conductor track37 extending beyond the notch 39 on the ceramic plate 34. The notch 39is arranged in such a way that when a force of a specific magnitude actson the lens 17 in the direction of the reflector 10 the ceramic plate 34is broken by the lens 17 which moves out of the holder 29 in its lowerregion as a result of the corresponding holder 36, as a result of whichthe conductor track 37 is interrupted. If the resilient ring 50 servesfor fixing the lens 17, the ceramic plate 34 can be arranged at a smalldistance from the lens so that during operation it is not subjected toany vibratory loads from the lens which could lead to an undesiredbreak. By means of a safety circuit of the control device 19, aninterruption of the conductor track 37 is detected and the operation ofthe gas discharge lamp 11 prevented. Thus, it is ensured that in theevent for example of a lens 17 which is damaged as a result of anaccident no UV radiation emerges from the headlamp and no parts at ahigh voltage can be touched. However, if only the front plate 18 isdestroyed and the lens 17 is still in its holder 29, the headlamp cancontinue to operate since the bond between the reflector, carrier andlens parts is still intact and no harmful UV radiation can emerge. Thecarrier 28 and the ceramic plate 34 and their electrical connections arecovered by the frame 31.

As a further safety measure, a voltage divider circuit which has tworesistors R1 and R2 at which a defined voltage drop occurs can bemounted on the ceramic plate 34. By means of the predetermined break,one of the lines of the voltage divider is interrupted so that thevoltage drop changes substantially in relation to the other branch ofthe voltage divider circuit and thus the fault is indicated. If avoltage drop which deviates from the predetermined voltage drop occurs,this is detected by the safety circuit of the control device 19 and theoperation of the gas discharge lamp 11 is prevented. Thus it isprevented that, for example due to short circuiting of the signallinglines 38, the gas discharge lamp 11 can be operated even when the lens17 is damaged.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in aheadlamp for motor vehicles, it is not intended to be limited to thedetails shown, since various modifications and structural changes may bemade without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A headlamp for motor vehicles,comprising a reflector; a gas discharge lamp; a front plate covering alight exit opening of the headlamp; a filter arranged in a beam path oflight beams reflected by said reflector and light beams transmitteddirectly to said front plate and at least partially absorbing light in aUV wavelength region; a shade arranged in the beam path of the lightbeam reflected by said reflector; a lens arranged in the beam path ofthe beams influenced by the shade and forming an image of an edge ofsaid shade as the light/dark border of a light distribution, said lensbeing formed as a filter; and a holder which holds said lens and has acomponent with an electrical line such that said electrical line isinterrupted when said lens impacts against said component with aspecific force, and operation of said gas discharge lamp is preventedwhen said electrical line is interrupted.
 2. A headlamp as defined inclaim 1, wherein said filter is formed as a disc-shaped filter.
 3. Aheadlamp as defined in claim 1, wherein said filter is formed as a discand arranged between said gas discharge lamp and said front plate.
 4. Aheadlamp as defined in claim 3, wherein said disc is coated with a UVlight-absorbing coating.
 5. A headlamp as defined in claim 3, whereinsaid disc is composed of a UV light absorbing material.
 6. A headlamp asdefined in claim 1, wherein said front plate forms said filter.
 7. Aheadlamp as defined in claim 6, wherein said front plate is providedwith a coating which absorbs light in the UV wavelength region.
 8. Aheadlamp as defined in claim 6, wherein said front plate is composed ofa UV light-absorbing material.
 9. A headlamp as defined in claim 1,wherein said lens is provided with a coating which absorbs in the UVwavelength region.
 10. A headlamp as defined in claim 1, wherein saidlens is composed of a UV light-absorbing material.
 11. A headlamp asdefined in claim 1, wherein said filter is provided with a metal coatingcomposed of a material selected from the group consisting of gold andchromium.
 12. A headlamp as defined in claim 1, wherein said filter isprovided in said fluoride coating.
 13. A headlamp as defined in claim 1,wherein said filter has a brownish coloring.
 14. A headlamp as definedin claim 1, wherein said filter absorbs light in a blue wavelengthregion.
 15. A headlamp as defined in claim 1, wherein said electricalline is formed as a conductor track mounted on said component, and thecomponent is broken in such a way by said lens when it impacts againstsaid component that said conductor track is interrupted.
 16. A headlampas defined in claim 1, wherein said component is composed of ceramic andprovided with a predetermined break point.
 17. A headlamp as defined inclaim 1, and further comprising an electrical control device having asafety circuit and signalling lines which connect said line to saidelectrical control device, so that prevention of the operation of thegas discharge lamp is performed by means of said safety circuit of saidelectrical control device when at least one of said line and saidsignalling line is interrupted.
 18. A headlamp as defined in claim 17,and further comprising a voltage divider circuit located in saidelectrical line, said electrical control device having an evaluationcircuit which prevents the operation of the gas discharge lamp in theevent of a voltage drop in said electrical line deviating from a voltagedrop predetermined by said voltage divider circuit.
 19. A headlamp asdefined in claim 18, wherein said voltage divider circuit is arranged onsaid component.
 20. A headlamp as defined in claim 1, wherein saidfilter is provided with a fluoride coating.
 21. A headlamp for motorvehicles, comprising a reflector; a gas discharge lamp; a front platecovering a light exit opening of the headlamp; a filter arranged in abeam path of light beams reflected by said reflector and light beamstransmitted directly to said front plate and at least partiallyabsorbing light in a UV wavelength region; a shade arranged in the beampath of the light beam reflected by said reflector; a lens arranged inthe beam path of the beams influenced by the shade and forming an imageof an edge of said shade as the light/dark border of a light beamreflected by said reflector; a lens arranged in the beam path of thebeams influenced by the shade and forming an image of an edge of saidshade as the light/dark border of a light distribution, said lens beingformed as a filter; a carrier which is connected with said reflector andformed as a hollow cylinder closed at its circumference, said lens beingarranged in said carrier, said carrier having a radially inwardlypointing edge; and a radially elastically resilient ring, said lensbeing held resting against aid radially inwardly pointing edge of saidcarrier by means of said radially elastically resilient ring which isinserted in said carrier.
 22. A headlamp as defined in claim 21, whereinsaid filter is formed as a disc-shaped filter.
 23. A headlamp as definedin claim 21, wherein said filter is formed as a disc and arrangedbetween said gas discharge lamp and said front plate.
 24. A headlamp asdefined in claim 23, wherein said disc is coated with a UVlight-absorbing coating.
 25. A headlamp as defined in claim 23, whereinsaid disc is composed of a UV light absorbing material.
 26. A headlampas defined in claim 21, wherein said front plate forms said filter. 27.A headlamp as defined in claim 26, wherein said front plate is providedwith a coating which absorbs light in the UV wavelength region.
 28. Aheadlamp as defined in claim 26, wherein said front plate is composed ofa UV light-absorbing material.
 29. A headlamp as defined in claim 21,wherein said lens is provided with a coating which absorbs in the UVwavelength region.
 30. A headlamp as defined in claim 21, wherein saidlens is composed of UV light-absorbing material.
 31. A headlamp asdefined in claim 21, wherein said filter is provided with a metalcoating compound of a material selected from the group consisting ofgold and chromium.
 32. A headlamp as defined in claim 21, wherein saidfilter has a brownish coloring.
 33. A headlamp as defined in claim 21,wherein said filter absorbs light in a blue wavelength region.